Western Brook Lampreys are typically found in large coastal rivers and their tributaries. Larval Brook Lampreys, or ammocoetes, are typically found in slackwater areas or pools where they burrow tail first into soft substrate. Burrowed ammocoetes feed on algae and organic matter passing in the water column. In an optimal habitat of sand and silt the ammocoetes might have a distribution as dense as 170 larval lampreys per square meter. The larval stage lasts 2-4 years in California but may last 4-5 years in British Columbia. Ammocoetes undergo metamorphosis in the fall and the resulting adults are ready to spawn by the following spring. Spawning takes place in riffles in the early spring and may last up to six months depending upon the flow regime of the stream. Adult spawners dig nests 15-20 cm long in a gravel substrate where one female may be surrounded by several males. The female releases 1,100-3,700 eggs, which are quickly fertilized, and then the nest is covered. The eggs hatch in about 10 days.